Yesterday bought Apple Battery Charger from DS, outer box looks bit old hence worried if the given product was not recently manufacture and as it has batteries i understand they have certain life period after manufacture date.
Do i need to worry about this ?

The charger detects when the batteries are full and stops.
The maximum charge time is 4.5hours if the batteries are empty.
If the two batteries are at different charge levels when they are inserted, each battery is finished separately. The indicator will indicate done when both batteries are finished.

This could be due to multiple reasons:
1) The batteries are faulty one way or another, are you charging the official Apple ones?
2) The charger is defective.
3) If the light is still orange then the batteries just plain aren't fully charged yet. Leave them in over night and if any light at all in on come morning, you'll know that option 1 or 2 is the answer. I say this because once the batteries charge, the light will turn green, but then the light will turn off completely eventually.

Yes. The AC wall prongs slip off just like on a Macbook power supply, enabling you to connect any of the plugs in the World Travel Adapter Kit. The charger will accept any voltage from 100-240V, making it suitable for worldwide use.

Based on the product page, yes, you should be able to:
"Thanks to an intelligent power management system, the Apple Battery Charger uses less power once your batteries are fully charged, making it one of the most energy-efficient rechargeable battery solutions ever."
However, for maximum life, you should not leave the batteries plugged in all the time.

Prices are inclusive of VAT (23%) and Insurance duties and levies (where applicable) but exclusive of delivery charges unless otherwise indicated. The VAT rate for products classified as services under EU VAT law will be 23% as VAT is charged at the rate payable in the country where Apple Distribution International supplies such products, which is the Republic of Ireland. The order form shows you the VAT payable on the Products you select. WEEE and battery registration number: IE 1807WB
Apple Distribution International is regulated by the Central Bank of Ireland and has permission to offer its services in certain EEA countries.
For further information, please see registers.centralbank.ie.